1. Field of the Invention
The invention relates to a process for emulsion polymerization of graft copolymers using a sulfonate group-containing, optionally crosslinked vinyl ester/ethylene copolymer as the graft base and grafting on one or more monomers other than ethylene and vinyl esters. The invention also relates to articles comprised of at least one thermoplastic polymer and the graft copolymer prepared by the process.
2. Description of the Related Art
A number of processes for graft copolymerization have been described. In DE-A 1,495,694 (U.S. Pat. No. 3,358,054), a process is claimed in which a vinyl acetate/ethylene (VAE) copolymer is employed in the solid state. The solid VAE copolymer is dissolved in the vinyl chloride monomer phase, dispersed in water and grafted using a suspension polymerization process. The time-consuming and expensive dissolution of the solid resin is disadvantageous in this process. Due to the rapidly increasing viscosity of the solution, it is difficult to achieve solid resin contents of greater than 15%. Due to the relatively large particle size which is associated with the suspension polymerization process, inhomogenity with respect to the copolymer composition can occur at short solution times.
In the process of DE-A 2,344,553 (U.S. Pat. No. 4,006,201), the graft base initially introduced is an aqueous vinyl acetate/ethylene dispersion. Vinyl chloride is metered in during the graft copolymerization. The production of the VAE dispersion and the grafting take place in the presence of a nonionic emulsifier and protective colloid. The product is produced with the consistency of suspension PVC. Using this procedure, a reduction in the reaction time is achieved due to the use of the VAE dispersion. However, the use of a H.sub.2 O-soluble protective colloid and a nonionic emulsifier has a deleterious effect. If a protective colloid is employed to stabilize the dispersion used as the graft base, products having high water sensitivity result. Due to the incompatibility of the protective colloid and graft copolymer, turbid molding compositions are obtained when the graft copolymers are processed. Nonionic emulsifiers, in particular ethylene oxide condensation products which are usually employed for stabilization of dispersions, result in thermal instability during thermoplastic processing of VC-grafted VAE copolymers; the products tend to discolor.
DE-A 2,104,870 (U.S. Pat. No. 3,856,733) describes the grafting of a vinyl acetate/ethylene copolymer latex with vinyl chloride under emulsion polymerization conditions. In this case, further emulsifier, specifically nonionic ethylene oxide condensates and a protective colloid, are added during the graft copolymerization in addition to the emulsifier and protective colloid present in the latex. Although inhomogeneities of the graft product are thus avoided due to the smaller particle sizes in the emulsion process, the above-described adverse effects with respect to processability and product quality again occur here due to the use of relatively large amounts of nonionic emulsifier and protective colloid.
The object of the invention is to provide a process for the production of graft copolymers, and articles prepared therefrom, in which a vinyl ester/ethylene latex is grafted, preferably with vinyl chloride, using the emulsion polymerization process without the above-described disadvantages with respect to processability and product quality occurring.